lca2020: use correct fonts

Signed-off-by: Sean Cross <sean@xobs.io>

css/theme/lca2020.css

@@ -100,7 +100,7 @@ body {
 }
 
 .reveal {
-    font-family: "Space Mono", Helvetica, sans-serif;
+    font-family: "IBM Plex Mono", "Space Mono", Helvetica, sans-serif;
     font-size: 42px;
     font-weight: normal;
     color: #212529;
@@ -136,7 +136,7 @@ body {
 .reveal h6 {
     margin: 0 0 20px 0;
     color: #212529;
-    font-family: "Montserrat", Helvetica, sans-serif;
+    font-family: "Brix Sans Medium", "Montserrat", Helvetica, sans-serif;
     font-weight: 300;
     line-height: 1.2;
     letter-spacing: normal;